The present invention relates to a seal between relatively movable members, preferably between first and second relatively rotatable members, in particular a rotor and a stator, more particularly to a seal between a rotor blade and a casing of a turbomachine, for example a gas turbine engine.
A compressor of a gas turbine engine comprises one or more stages of compressor rotor blades arranged alternately with one or more stages of compressor stator vanes. Each of the compressor rotor blades comprises a root, a shank, and an aerofoil. The compressor rotor blades are arranged circumferentially around a compressor rotor and the compressor rotor blades extend radially from the compressor rotor. The roots of the compressor rotor blades are located in axially, or circumferentially, extending slots in the periphery of the compressor rotor. The platforms of the compressor rotor blades together define the inner boundary of a portion of the flow path through the compressor. In an alternative arrangement the compressor rotor blades are integral with the compressor rotor and are either machined from a solid disc of metal or are friction welded, electron beam welded or laser beam welded to the compressor rotor.
The compressor rotor and compressor rotor blades are surrounded by a compressor casing. A small gap, or clearance, is provided radially between the tips of the compressor rotor blades and the compressor rotor casing. The compressor casing is provided with an abradable coating on its radially inner surface immediately around the tips of the compressor rotor blades. These abradable coatings wear preferentially relative to the material of the tips of the compressor rotor blades during engine service. The abradable coatings reduce over tip leakage between the tips of the compressor rotor blades and the compressor casing and hence reduce the associated loss in engine efficiency and engine performance.
Abradable coatings are also used on the turbine casing, which is arranged radially around stages of turbine rotor blades. Abradable coatings are also used on other components of gas turbine engines.
Abradable coatings are used where there is a requirement to form a seal between a rotatable or movable component and a static component.